I highly doubt that it would fail an MOT for missing the brackets, the chances of the MOT tester knowing that they should be there and noticing that they are not is quite slim, the brackets are there I believe to prevent scuttle shake from the now weakened dash and windscreen surround. Tbh I would start to be thinking if the dash brackets have been omitted, have other more important parts such as the vital sill strengtheners not been fitted as well? Shame as it seems a lovely car
Also calling it a 58 is off with the turn signal and horn push design, and the smaller, oval number plate wasn't used until later 59, so 1/59 is a stretch. No trafficator slots but the wiper locations match. Carb also updated to HS2. What's going on with the heater hoses? Where is the one on the spark plug side of the engine going?
The heater take off appears to have been fitted into the temperature gauge take off which is above the thermostat.
In that configuration the water pump will not push any water round the heater.